1. Field of the Invention
The present invention relates to an ultrasonic wave linear motor provided for the purpose of obtaining linear displacement by employing the ultrasonic wave oscillation of a piezoelectric element as a drive power supply.
2. Description of the Prior Art
Recently, an ultrasonic wave motor has been developed with ultrasonic oscillation of a piezoelectric element made of piezoelectric ceramics used as its driving power supply, and used as an actuator for various kinds of apparatus. A compact size and high torque are expected to such an ultrasonic wave motor which possesses such merits as no influence on electromagnetic medium etc. owing to no generation of electromagnetic waves.
In the ultrasonic wave motor, the oscillation of a drive body in its feed direction is arranged to be transmitted to a driven body by aid of friction by placing the oscillatory drive body in the vicinity of the driven body. The oscillation of the drive body is in form of either a slant linear oscillation composed of mutually orthogonal oscillatory components or an elliptical oscillation. Therefore, the drive body can be classified in three types, that is, an oscillatory piece type, a torsional oscillator type and an advance wave type.
The ultrasonic wave motor of oscillatory piece type drives in such a manner as shown in FIG. 44 that a piezoelectric oscillator 111 making longitudinal oscillation and an oscillatory piece 112 attached thereto are set slant to the contact surface of a driven body 113 so as to push the driven body 113 in a fixed direction so that high speed operation can be carried out with high conversion efficiency.
The ultrasonic wave motor of torsional vibrator type is formed in such a manner, as shown in FIG. 45, that an elliptical oscillation may be generated instead of the linear oscillation of the oscillatory piece type by attaching a torsion coupling element 115 to a piezoelectric oscillator 114.
The advance wave type ultrasonic motor forces a contact surface with a rotor 118 to make an elliptical oscillation, by coupling a piezoelectric element 117 to an oscillatory body 116 formed in an annular shape or a disc shape and giving a flexural oscillation wave advancing in the circumferential direction to an oscillatory body 116 as shown in FIG. 46, and this motor possesses such a merit as small wear due to a large contact area.
However, the above-mentioned every prior art has involved such tasks to be solved as follows.
Firstly, in the case of an oscillatory piece type ultrasonic wave motor, the oscillation is unstable and the direction for sending a driven body is fixed, because the contact between the oscillatory piece 112 and a driven body 113 is intermittent. Furthermore, a rotor oscillatory piece 112 involves such a problem as severe wear of its tip.
A torsional oscillatory piece type ultrasonic wave motor involves such drawbacks as difficulty, from view of its structure, to control oscillation for feeding and oscillation for controlling friction separately and to require a linear motion conversion mechanism so as to be used in form of a linear motor.
And an advance wave type ultrasonic wave motor has such drawbacks as requiring a linear conversion mechanism as stated above as well as low efficiency of energy conversion. Meanwhile, it can be taken into account, in the case of an advance wave type ultrasonic wave linear motor, that a linear oscillatory body is installed instead of an annular or disc-shaped oscillatory body 116 so as to transmit the oscillation to a driven body by applying the advance wave thereto, but it may involve, in this case, such drawbacks as increasing the energy loss to deteriorate the concerned efficiency because of excitation of advance wave required on the total length of a rail.